1. Field of the Invention
The present invention relates to a semiconductor device and to a method for manufacturing the same. In particular, the present invention relates to a groove, which is disposed on a heat sink, for preventing solder from flowing out.
2. Description of the Related Art
FIGS. 9A and 9B show a schematic view of a conventional semiconductor device 500. FIG. 9A is a plan view thereof. FIG. 9B is a magnified sectional view cut along the line X-X in the FIG. 9A. FIGS. 9A and 9B illustrate a heat sink 51 on which a groove 55 is disposed and an insulating substrate 52 fixed to the heat sink 51 with solder 53. An insulating plate such as ceramic, a back surface copper foil stuck on the back surface thereof, and front surface copper foils forming a circuit pattern stuck on the front surface thereof constitute the insulating substrate 52. A semiconductor chip not shown is fixed to the front surface copper foil. The back surface of the insulating substrate 52 is fixed to the heat sink 51 with the solder 53.
In FIGS. 9A and 9B, each one of a plurality of (two in this case) insulating substrates 52 is fixed at each one of predetermined arrangement areas on the heat sink 51. A mother material 50 composed of aluminum or the like and a nickel layer 54 coating the surface thereof to ensure solder wettability and to avoid oxidation constitute the heat sink 51. The nickel layer 54 is composed of a nickel plating layer or the like.
On the assembly process of the semiconductor device 500, if the plurality of insulating substrates 52 are fixed to the heat sink 51 with solder 53, there may be such a case that adjacent pieces of molten solder are in contact with each other to run on to the front surface of the insulating substrate 52. Then insulation failure will occur at the spot where the solder has run on. To avoid such circumstances, it is carried out that one groove 55 is disposed around the area where the insulating substrate 52 will be arranged on the surface of the heat sink 51, preventing molten solder from flowing out as described in Japanese Patent No. 2500669, and Japanese Unexamined Patent Application Publication No. 2008-159857.
Mounting the plurality of insulating substrates 52 on one sheet of the heat sink 51 may require that the width of the groove 55, which becomes a dead space, decreases as narrow as possible, and then the insulating substrate 52 mounted on the heat sink 51 increases in number. On the other hand, if the width of the groove 55 decreases excessively, solder can flow out from the groove 55. Then the problem that the adjacent pieces of molten solder are in contact with each other may occur as described earlier.